Warning: Don't read other posters' comments unless you give up since it usually contains the answer. An old eccentric wealthy man is giving a quiz competition. Whoever can guess the quiz correctly will inherit his house for free. Inside his house is one particular strange room. This room has no windows at all. There is only one door leading to this room. Inside this room there are three lightbulbs, in addition to basic furnitures like chairs, table, etc. Outside the room there are three switches, each one control a particular lightbulb inside. All of the three swiches are at Off position. The quiz works as follows: You may turn the switches anyway you want to. You then go inside the room "only once", and you must be able to tell which switch controls which lightbulb. How would you do it?
Good question. Is there a time-limit here? If not, I would turn Switch #1 on, leave it on for an hour, turn it off. Turn Switch #2 on. Then go into the room. One of the lightbulbs should be on - that would be #2. Another should be off, but cold. That's #3. The third should be off, but warm. That's #1. If you can't wait a while for a bulb to heat up, I dunno.
Turn on one of the switches for a long period of time. Then I would turn it off and turn another on. Go into the room, the one that is lit tells you about one switch, the one that is off, but hot tells you about another and the light bulb that is off and cold tells you about the 3rd.
Leave one switch off. Turn one on. Turn the last one on, wait several minutes, then turn it off. Go into the room. The bulb that is lit is the one with the switch on. The cool dark one is the bulb you never turned on. The warm dark one is the bulb that was on for several minutes.
